Effects of carbaryl, permethrin, 4-nonylphenol, and copper on muscarinic cholinergic receptors in brain of surrogate and listed fish species

Abstract

We investigated the regulation of the muscarinic cholinergic receptor (MChR) in brain from seven species of fish, two surrogates and five threatened or endangered species exposed to a series of chemicals as a measure of compensatory response among species. Fish were classified as either cold water (rainbow trout-surrogate, apache trout, lahanton trout) or warm water (fathead minnow-surrogate, razorback sucker, bonytail chub, colorado squawfish) and were exposed to chemicals shown to affect cholinergic pathways (carbaryl and permethrin) and two chemicals whose relationships to the cholinergic system is less clear (4-nonylphenol and copper). Downregulation of MChR occurred in all warm water species, except colorado squawfish, and at carbaryl concentrations similar to those causing downregulation observed in rainbow trout. Permethrin exposure resulted in downregulation in fathead minnow and razorback sucker, but the concentrations required for observation of this phenomenon were much greater than observed in cold water species. Copper exposure caused a decrease in brain MChR in rainbow trout and apache trout, whereas 4-nonylphenol exposure resulted in a decrease in brain MChR in all three cold water species. Our results indicate that surrogates are useful in assessing sublethal physiological responses to chemicals with a known mechanism of action such as carbaryl and support use of surrogates for assessing physiological responses to chemicals with diverse, less clear mechanisms of action.

Reproductive effects of prenatal exposure to nonylphenol on zebrafish (Danio rerio)

“…Nonylphenol and related compounds are metabolized by fish (Cravedi and Zalko, 2005) and exert numerous direct and indirect effects in fish species, ranging from changes in gene expression (Larkin et al, 2003;Arukwe et al, 2001Arukwe et al, , 2002 through induction of estrogen responsive genes (Arukwe et al, 2001(Arukwe et al, , 2002 and protein (Andreassen et al, 2005) and effects on brain muscarinic receptors (Jones et al, 1998) to increased apoptosis (Weber et al, 2002), expression of acute phase protein (Baldwinm et al, 2005) and changes in phase II detoxication (Hughes and Gallagher, 2004).…”

Cholinergic and Behavioral Neurotoxicity of Carbaryl and Cadmium to Larval Rainbow Trout (Oncorhynchus mykiss)

“…Downregulation of MChR in response to carbaryl and to copper has been demonstrated in rainbow trout (RBT; Jones et al, 1998). Receptor downregulation is an adaptation, which, by providing fewer active receptors for ACh to stimulate, may allow return to normal behavior.…”

A comparison of β‐adrenoceptors and muscarinic cholinergic receptors in tissues of brown bullhead catfish (Ameiurus nebulosus) from the black river and old woman creek, Ohio

“…Thus, the decrease in receptor number could be interpreted as a stressor response brought about by exposure to PAHs. This would be similar, albeit a different mechanism, to the downregulation of brain MChRs that occurs in rainbow trout following carbaryl exposure [8]. An alternative explanation could be that the decreased number of receptors is a consequence of generalized toxicity of the fish from the Black River.…”

“…Each of these receptor types can be measured in membrane preparations of tissue in which these receptors are present. Changes in concentration of endogenous neurotransmitters or exposure to xenobiotics can cause a decrease (downregulation) or increase (upregulation) in receptor number in a variety of tissues, including fish brain and erythrocytes [6,8]. These compensatory responses by the cells occur to preserve a level of homeostasis that is compatible with normal function.…”